Rigid recording disk cartridges having a circular, floppy magnetic or optical disk rotatably mounted within the disk cartridge case are well known. The cartridge is mountable on a disk drive apparatus to rotate the recording disk and access the disk by a magnetic or optical recording head for recording or reproducing information. The disk cartridge includes a rotatable magnetic or optical disk, a cartridge case for housing the magnetic disk having a central axis and a front peripheral edge, and a U-shaped shutter slidably disposed on the front peripheral edge of the case.
The cartridge case includes generally rectangular upper and lower walls which mate to form the outer dimensions of the cartridge case. A drive shaft opening is formed through a central portion of the lower wall to receive a drive shaft to rotate the magnetic disk within the cartridge case. A head access opening is formed in both the upper and lower walls between the central axis and the front peripheral edge to access the magnetic disk. The head access opening is opened and closed by the shutter which slides between open and closed positions. A spring biases the shutter in the closed position to cover and close the head access opening. When the cartridge is inserted into the disk drive, the shutter is moved to the open position by the disk drive to provide access to the disk. The shutter may also include one or more tabs which ride in a slot in the wall of the cartridge to guide the shutter.
A shallow indented portion is formed on both the upper and lower walls for receiving the shutter. Each indented portion is defined by a U-shaped edge on a respective wall. The portion of each U-shaped edge at the side toward which the shutter is biased serves as a stop for the shutter when the shutter is biased closed. However, when the cartridge is removed from a disk drive and the shutter is biased to its closed position, the shutter tends to slide past the edge as there is not sufficient interference between the edge and the shutter. This problem is particularly acute with plastic shutters, which deform more easily than metal shutters. When the cartridge is next inserted into the disk drive, the displaced shutter may interact incorrectly with the drive, which can result in damage to the cartridge and data loss.
This shutter displacement frequently results from the cartridge being dropped during handling. One edge of the shutter can ride over the U-shaped edge to encompass the thicker portion of the case. This can prevent the shutter from opening upon insertion into the disk drive or prevent the cartridge from loading into the drive.
European Patent Application Publication No. 264,237 discloses a disk cartridge in which the shutter can slide to either side of the head access opening. Abutting plates 35A and 35B serve as anchoring points for opposing torsion springs which push the shutter toward the center of the cartridge to close the cartridge. The shutter does not stop against the cartridge and these plates do not extend to the ends of the shutter slide area as the shutter must be able to slide to both sides of the head access opening.
European Patent Application Publication No. 218,231 discloses a disk cartridge in which the shutter stops against a stopper 5 to prevent the shutter from opening inadvertently. However, the stopper does not work with the shutter engagement mechanism used in 3.5 inch microfloppy disk cartridge drives. With 3.5 inch disk cartridges and drives, an engagement pin in the drive slides the shutter open from right to left, as viewed from above, as the cartridge is inserted in the drive. As the cartridge is ejected from the drive, a torsion or extension spring forces the shutter to the right until it contacts a vertical ridge approximately 0.203 mm (0.008 in) to 0.356 mm (0.014 in) deep in the cartridge case. The ridge stops the shutter and the shutter is held against the ridge by the spring. This ridge is small relative to the shutter and cartridge manufacturing tolerances. If the shutter is too wide and the mechanical interference between the shutter and the cartridge is too small, the shutter can override the ridge and becomes stuck on the cartridge. When the shutter is next inserted into the drive, the engagement pin cannot open the shutter and the cartridge will not function and may stick in the drive. With resin-based shutters, the probability of shutter override is greater as the flexural modulus for resins is much lower than for steels.
Neither of these disclosures addresses the problem of preventing shutter misalignment in 3.5 inch microfloppy disk cartridge drives. There is a need for a shutter stop mechanism which prevents such shutter misalignment.